1. Field of the Invention
The present invention relates to slot array antennas. More specifically, the present invention relates to an improved feed for a slot array antenna.
While the present invention is described herein with reference to an illustrative embodiment for a particular application, it is understood that the invention is not limited thereto. Those of ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope thereof.
2. Description of the Related
Planar array antennas are used for a wide variety of radar applications. One such planar array antenna is a flat plate antenna. A flat plate antenna is typically a family of coplanar linear arrays each containing a series of resonant slot radiating apertures. Microwave energy is provided to the radiating waveguides by a feed waveguide which is in turn fed by an input waveguide.
Slot coupling is a desirable technique for coupling energy from the feed waveguide to the radiating waveguides for most applications. Slot coupling, for a single feed, involves communication of energy through a slot in a broadwall of a rectangular feed waveguide and slots in a broadwall of a rectangular radiating waveguide. Energy is typically provided to the feed waveguide by an input waveguide located at either end of the feed waveguide or somewhere along the length thereof. The location of the input waveguide at the ends of the feed waveguide may limit the bandwidth of the system or be otherwise problematic because of the relative inaccessibility of the ends of the feed waveguides.
The center feeding of the feed waveguide is problematic with respect to the location of the input slot of the input waveguide relative to the feed slot of the feed waveguide. That is, if, as is common, the input slot and the feed slots are placed on opposite broad walls of the feed waveguide and at one-quarter wavelength spacing down the waveguide, an impedance inversion results on each half of the feed waveguide which must be corrected in the design. A common technique for correcting the impedance inversion involves a design in which coupling slots are at greater angles. Unfortunately, this approach typically results in larger coupling junction phase errors.
Location of the input slots on the opposite broadwall at the same position along the length of the feed waveguide as the feed slots has heretofore been avoided because of difficulty in achieving independent coupling of the input slot and the opposite feed slot.
There is therefore a need in the art for a planar array antenna feed waveguide which has an input slot located between the ends of the waveguide but does not have any associated impedance inversion.